I'm not suggesting that smoking or drinking are the cause of the allergies but I wonder if they put additional stress on the liver, kidneys etc. Maybe it's the case that Psoriasis is an allergic reaction to toxin build-up?
Strangely enough, I've found that my Psoriasis gets worse if I eat a healthy diet. It calms down quite rapidly if I don't eat fruit and veg for a few days - I'm sure this can't be doing me any good!
I'm curious to know what sort of diet you've found beneficial, if you wouldn't mind telling me.